A new fossil from the age of the dinosaurs suggests modern crocodiles originated in Queensland, not Europe or North America as previously thought.

An international team of palaeontologists say fossils discovered in the central-western Queensland town of Isisford are that of the world's most primitive modern crocodile.

The report on the fossilised remains of the most primitive ancestor of modern crocodiles, has been published in the Royal Society journal Proceedings B.

Team member Dr Paul Willis, an honorary research associate at Sydney's University of New South Wales and presenter on ABC TV's Catalyst program, says until now the crocodiles were thought to have originated from Belgium, England and the USA.

But Dr Willis says the new specimen, Isisfordia duncani, shares more features in common with modern crocodiles than any specimens found in the northern hemisphere.

The researchers say that, at 98- to 95 million-years-old, Isisfordia predates modern crocodiles by about 20 million years.

"Ours is the grand-daddy of crocodiles," Dr Willis said.

Ball and socket joints

Modern crocodiles are defined by having ball and socket joints between their vertebrae.

Dr Willis says this gives them a very flexible yet strong backbone.

"Crocodiles have incredible bursts of very violent energy and so you need a strong backbone to be able to withstand that," he said.

Dr Willis says modern crocodiles also have a hard palate that reaches right to the back of the mouth, which means they can breathe at the same time as eating something under water.

The palate also strengthens the snout, bracing it and distributing forces when the crocodile bites something.

"Crocodile bites are second only to tyrannosaurus as the most powerful known bites of all time," Dr Willis said.

Dr Willis says all these features would have given Isisfordia and its descendants greater evolutionary advantage than its predecessors in aquatic environments.

Complete skeleton

Dr Willis and colleagues have analysed two fossilised skeletons first discovered in the mid-1990s in a creek bed in Isisford, in central-western Queensland, by the former deputy mayor of the town, Ian Duncan.

One specimen is almost a complete skeleton with just the snout and face of the crocodile missing. The other is a complete skull.

"Between the two we have a complete skeleton. We know what the whole animal looked like and it's very rare to get that," he said.

The researchers know the two are from the same species because they have the back of the skull of both.

Small crocodile

Dr Willis says Isisfordia was a small crocodile, only a metre long, weighing around three or four kilograms.

He says it was the only known crocodile in Australia at that time and would not have had much competition.

Dr Willis says it would have lived in a swampy river delta that opened into a large inland sea and survived on eating, among other things, fish and other small vertebrates, insects and crustaceans.

Dr Willis says Isisfordia would have been the most immediate ancestor of all modern crocodilians.

This includes crocodiles, alligators and creatures such as gharials (long thin-snouted crocodiles that live in the Ganges River) and caimans (close relatives of alligators from South America).

Gondwana overlooked

Dr Willis says this is not the first time that Gondwana has been overlooked as a site of evolution.

"The fossil record is loaded to the northern hemisphere because there are more sites and more people looking for fossils," he says.

"But as we're finding more fossils in the Gondwanan continents it appears that a lot of groups that we previously thought originated in the northern hemisphere - or in Laurasia - actually have older representatives here in the southern continents, and in this case in Australia."